1. Field of the Invention:
The present invention relates to a filter-press type electrolytic cell formed by alternatively arranging the frames and the ion-exchange membranes and fastening them.
More particularly, it relates to a filter-press type electrolytic cell for producing caustic alkali by an electrolysis of an aqueous alkali metal salt such as an alkali metal chloride.
More particularly, it relates to a filter-press type electrolytic cell wherein a saturated solution of sodium chloride or like is fed into the anolyte compartment and water or a dilute solution of sodium hydroxide is fed into the catholyte compartment, and the electrolysis is attained to obtain chlorine and a dilute solution of sodium chloride from the anolyte compartment and to obtain a concentrated solution of sodium hydroxide (20 to 40 wt.%) and hydrogen gas from the catholyte compartment.
2. Description of the Prior Art:
In the electrolytic cell which is one of the filter-press type electrolytic cells, the frames having an anode, the ion-exchange membranes and the frames having a cathode are alternatively arranged and fastened to form anolyte compartment and catholyte compartment which are respectively partitioned with the membrane.
A solution should be fed and discharged through the frames for the electrolytic compartments such as the anolyte compartments and catholyte compartments, in the operation of electrolysis.
The frames for the conventional electrolytic cell are formed by plates made of synthetic resin having a central opening and a plurality of surrounding holes so as to communicate the corresponding holes in alignment for the compartments in the case of arrangement and fastening of the frames and have groove for communicating the holes and the electrolytic compartments, as disclosed in U.S. Pat. No. 3,869,375; U.S. Pat. No. 3,017,338 and U.S. Pat. No 3,933,617. When the solution is fed to the electrolytic compartment or is discharged from it, the solution is passed into the holes communicating through the frames at the bottoms of the frames and is fed through the groove to the electrolytic compartments. The electrolyzed solution or gas is passed through the groove into the holes communicating through the frames at the upper parts of the frames and is discharged through the communicating holes.
In order to form said grooves and holes on the frames, high processing accuracy and complicated processing operation are required and the work is not easy and the cost is expensive.
It is disadvantages to use block type frames made of anticorrosive metal from the viewpoints expense and weight.
In the ion-exchange membrane electrolysis, the heat is generated by the electric resistance of the solution and the ion-exchange membrane in the compartments during the electrolysis whereby the liquids in the compartments are heated to about 80.degree. to 120.degree. C. It is required to use the frames which are heat resistance to prevent the deformation. In the case of the ion-exchange membrane electrolytic cell, the frames made of the synthetic resin is not suitable, and the frames made of superior metal should be used.
The frame of the filter-press type electrolytic cell using asbestos fabric has been known in U.S. Pat. No. 3,836,448. In the frame, the upper zone(2) for gas-liquid separation is formed at the upper part of the frame. The channels(5) are formed at the both side parts and lower part of the frame. The upper zone(2) is connected to the channels.
As shown in FIG. 2, the electrolyte is fed from the compartment to the upper zone wherein the gas is separated and the liquid is recycled through the channel to the compartment. From the viewpoint of whole of the electrolytic cell, the saturated aqueous solution is fed into the anolyte compartment to be electrolyzed. The most of the solution is fed through the asbestos membrane into the catholyte compartment. From the catholyte compartment, an aqueous solution containing sodium hydroxide and sodium chloride is discharged.
The channel(5) of the side part of the frame is fine. The circulation of the solution in the frame is not so large because of the pressure loss. The volume of the upper zone for the gas-liquid separation need not so large. However, in the ion-exchange membrane electrolytic cell, the feeding and discharging of the solution is attained in each compartment as described above. The product of the electrolysis is obtained from the upper parts of the compartments. Accordingly, when the frame is used as the frame for the ion-exchange membrane type electrolytic cell, the volume of the solution fed into the upper zone of the frame is increased in the comparison with the conventional asbestos diaphragm method. In order to attain suitable gas-liquid separation, the volume of the upper zone should be large.
From the viewpoint of the strength of the upper zone of the frame, it is necessary to increase the thickness of the frame. Accordingly, when the conventional frames are used as the frames of the ion-exchange membrane type electrolytic cell, the size of the cell should be too large from the viewpoint of the characteristics. The frame should be made of a metal and the weight is too heavy.